Hyperspectral Features Of Crop Affected By Frostbite And Monitoring With Remote Sensing

Because of the limitness of natural resource and economic condition,the food production depends on the weather and climate strongly in China.Drought, flood and frostbite are the main weather disasters during the crop development.The influence of drought and flood were wide and serious, whose real-time monitoring with remote sensing applied early and had achieved many accomplishments. Reversly, the danger of frostbite was minor, but in some serious years, the affected area and the loss of yield were tremendous. The food security faces great threat and it has attracted wide attention, so it is very important to real-time monitoring the crop growth and to make prediction of crop production for policy making and sustainable development.At the present, the crop monitoring and prediction of production draws great attention all the time in not only developing country but also developed country.The result of the frostbite disaster often depends on the observation in filed, which is arduous and wasting time, the result is subjective and the scope of the observation is small, moreover, because the concealment and delay of the harmness to the crop, which result to undervalue the affected area and frostbitten degree.The merits of remote sensing possessed include in the extension of monitor, information update quickly, objectively, lower cost and free to location, which make it is one of the most promising methods to monitor crop growth.The weather or not of frostbite disaster occurrence depends on the crop itself and the low temperature and duration. However, it is difficult to reflect the duration with remote sensing, so the research of low temperature injury and frostbite monitor always focus on the temperature retrieval, area and distribution of crop planting, and evaluation of loss.With the application of hyperspectral remote sensing and high space resolution sensor and the advancement of precision of canopy temperature retrieval, it is possible to monitor frostbite in terms of the difference of vegetation index and canopy temperature. So in this paper, we conducted a pot experiment with the artificial frost box to simulate frostbite in 2006-2007 cotton breeding and winter wheat shooting season, researched the relationships among hyperspectral curves and crop growth characteristics after frostbite, to supply the transcendent knowledge for the monitoring frostbite with remote sensing. Combined the statistical data of agriculture disaster,crop development, production yield, agrometeorological observation data, and other accessorial data, applied to two temporal LANDSAT TM images in 1998-3-16 and 1998-4-17,to monitor the frostbitten of winter wheat which happened in east-north of Henan province in 1998-3-22, applied to ETM images in 2000-8-10 , 2001-6-7 and 2001-8-7 to monitor the frostbitten of cotton which happened in xinjiang shawan county in 2001-8-1. The main results as follows:(1)Frostbite affected the crop activity seriously, there is remarkable correlation between frostbite degree and agriculture parameters. With the temperature decrease and the frostbite degree deepen, the chlorophyll content, photosynthesis and transpiration rate became weaken, the stomatic conduction reduced and the leaf temperature increased.(2)Frostbite influenced the hyperspectral reflectance curve of leaf or canopy. For cotton, there is a minor difference in type of curve and reflectance value between treatments and control group's. It is difficult to exhibit the frostbite degree based on the difference, which contradict the appearance in treatments'crop. For winter wheat, in the early stage after frostbite, the reflectance and shape of hyperspectral curves were similar between treatments, after 20 days, the interior damage began to occurrence, frostbitten leaves turned into yellow in advance of CK, the shape of curves became plane.(3)There is notable correlation between frostbite degree and value at special positions in hyperspectral reflectance curve, vegetation index(NDVI), whose quantitative relationship supplied the experiential knowledge for frostbite monitor with remote sensing.(4)When applied the ETM images to monitor cotton frostbite in Blooming~Split boll stage, the difference of vegetation and canopy temperature are according with the experiment results. In terms of the vegetation index or canopy temperature can make sure of the zone of frostbite and grade the frostbite degree.(5)When applied TM images to monitor winter wheat frostbite at jointing stage, based on the difference of vegetation can make sure of the frostbitten zone, which is according with the statistical data. The difference and spatial distribution of the retrieval canopy temperature isn't according with the experiment conclusion, it need research deepen about confirm the frostbite degree based on the canopy temperature.